When you use a dialog box with many items to fill out, only one of the items can be accepting input from the keyboard at a time. The active item is said to be the item with the focus. You can press the TAB key to move the focus to the next item; press SHIFT+TAB to move the focus to the previous item. The item with the focus will usually have a dashed border around it, or it will have a blinking text cursor in it.